EP0666980B1

EP0666980B1 - Automated capillary electrophoresis apparatus

Info

Publication number: EP0666980B1
Application number: EP92920210A
Authority: EP
Inventors: Norberto A. Guzman
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-08-28
Filing date: 1992-08-27
Publication date: 2002-05-02
Anticipated expiration: 2012-08-27
Also published as: TW231314B; CA2120251A1; WO1993005390A1; AU2640192A; MX9204974A; DE69232592D1; AU661241B2; EP0666980A1; DE69232592T2; US5202010A; EP0666980A4

Abstract

Apparatus comprises an analyte concentrator (760) (one or more) for insertion into a capillary tube (770) and containing various structures (776) for carrying chemical substances (766) in the flow path for attraction or repulsion of samples passed through the capillary.

Description

The invention relates to a capillary electrophoresis apparatus comprising a capillary tube of the type which can be electrically charged, said capillary tube having first and second ends, first means at said first end of said capillary tube providing a source of substance to be transmitted through said capillary tube, second means coupled to said apparatus for applying electrical potential across said capillary tube whereby a sample flows through said capillary tube and past a detector, and said first means includes a rotatable table carrying a plurality of sample cups and a holder for holding an end of said capillary tube in operative relation with one of said cups. The invention relates furthermore to an analyte concentrator for use with capillary electrophoresis apparatus and a capillary electrophoresis apparatus comprising a capillary tube means of the type which can be electrically charged.
Capillary electrophoresis apparatus of this kind are known from WO 89/04966 A1.

BACKGRUND OF THE INVENTION

Electrophoresis is a phenomenon in which charged particles move in a conductive buffer medium of fluid across which a potential difference is applied. The migration is toward an electrode carrying charge opposite to that of the particles.
Electrophoresis is one of the most important methods available for the investigation of biological materials, and probably the most efficient procedure for the separation and detection of proteins and other matter.
Electrophoresis separation relies on the differential speeds of the migration of differently charged particles in an electrical filed. The migration speed is primary a function of the charge on the particle and the filed strength applied and the charge on a particle is determined by the pH of the buffer medium. The most important application of this technique in biomedical research and clinical chemistry laboratories, is in the electrophoretic separation of proteins, nucleic acids, their component peptides and oligonucleotides, as well as complex macromolecules such as lipoproteins.
Several different systems are known for practicing electrophoretic separation. For example, one system known as zonal procedures, has advantages but it also has certain limitations. Some of the most common limitations are: The amount of sample required in order to reveal the components by the common staining procedures is usually large, the preparation of the apparatus and complete system involved in the electrophoretic separation is commonly tedious and time consuming, the time required to obtain complete separation of the components is often hours, the time required to reveal the components and to obtain some quantitation of the separated substances is also commonly hours, the yield of recovery of the components as biological actives in most cases is very low, the reproducibility of the electrophoretic separation is not 100 percent accurate, and the automation to perform the entire system operation is almost lacking.
Capillary electrophoresis has been shown to be a technique for obtaining high separation efficiency. For some proteins and small peptides, separation efficiencies of approximately one million to about a few million have been demonstrated. In general, this technique utilizes a fused silica (quartz) capillary with an inside diameter ranging from about 25 microns to about 200 microns, and a length ranging from about 10 centimeters to about 100 centimeters. Since the entire volume of the column is only 0.5 to about 30 microliters (yielding probably the smallest total surface area of column chromatography), the injection volume is usually in the low nanoliters range. As a consequence, the sensitivity of this technique is quite high and it is possible to obtain quantitation in the order of picomoles (and probably femtomoles or attomoles) using fluorescence, electrochemical, laser-induced fluorescence, and mass spectrometry detectors, and to obtain quantitation in the order of nanomoles using ultraviolet detectors.
In capillary electrophoresis, the efficient heat transfer from small diameter capillaries permits application of unusually high voltages ranging from about 5,000 volts to about 30,000 volts while maintaining a low current, in the range of about 10 microamperes to about 90 microamperes. The application of high voltages promotes more effective separations and increases the speed of analysis to record times of about 5 to 40 minutes.
In addition to high separation efficiency (theoretical plates), fairly high resolution, high sensitivity quantitation, and small migration (retention) times, capillary electrophoresis presents a few more advantages over conventional electrophoresis and, in general, other chromatographic procedures. Some of these advantages are: a) application to a wide variety of samples ranging from small ions to proteins or other macromolecules of molecular weights of approximately 290,000 daltons or higher (such as DNA fragments, viruses, and subcellular particles) by using essentially the same column and probably the same conditions of electrophoretic separation; b) capillaries should provide an ideal system to explore nonaqueous media, particularly with substances which are highly hydrophobic; c) capillaries are reusable many times making the electrophoretic separation system very practical and economical; d) on-line electronic detection permits good quantitation and further enhances possibilities for fully automatic operation making the capillary electrophoresis system of higher resolution, greater speed, and better accuracy than conventional methods.
In the prior art, it is generally known that a material, containing mixtures of substances to be analyzed, can be passed along a capillary tube and through a detector under the influence of an applied voltage. The applied voltage charges the substances and the charges on the substances determine their spacing and their speed of passage along the capillary tube.
The prior art, U.S. Patents 3,620,958, 3,948,753 and 4,459,198, show electrophoresis apparatus including a capillary tube connected between two containers for containing the substance to be analyzed and having electrical potential applied between the two containers and across the capillary tube. While the various forms of apparatus shown in these patents are apparently useful, they require large concentrations of samples to be analyzed and none is capable of being automated or provides teaching related to automation.
The present invention provides high voltage capillary electrophoresis apparatus including, among other things, means for feeding small concentrations of sample material into a capillary tube, automatically applying the proper voltage to cause the components of the sample to be charged and to flow along the capillary tube through a detector wherein the components are detected and a printed record is made. The apparatus can then automatically repeat the process for the analysis of multiple samples.
The basic apparatus of the invention is susceptible of many modifications in its various parts including the capillary tube portion. In addition, the method of detection of samples may be varied and the collection of samples can be modified. The invention can also be adapted to measure electroosmotic flow in a capillary.

DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of the rear of apparatus embodying the invention;
Fig. 2 is a sectional view along the lines 2-2 in Fig. 1;
Fig. 3 is a side sectional view of the modification of a portion of the invention;
Fig. 4 is a side sectional view of the modification of the apparatus of Fig. 3;
Fig. 5 is a prospective view of another modification of the invention; and
Fig. 6 is a prospective view of a modification of a capillary tube assembly used in the apparatus of the invention.
Fig. 7 is a side view of another modification of the invention.
Fig. 8 is a side elevational view of a modified capillary including means for cleaning the capillary.
Fig. 9 is a perspective view of a modified capillary cartridge usable with the apparatus of the invention;
Fig. 10 is a perspective of apparatus embodying modifications of the invention.

DESCRIPTION OF THE INVENTION

The automated electrophoresis apparatus of the invention 10, shown from the rear in Fig. 1, includes a base support member to which various pieces of operating equipment are secured. The support member 20 is box-like and includes a top wall 30, a front wall 40, a rear wall 50 and end walls 60 and 70 all of which extend downwardly from the top wall. A bottom cover plate 80 (Figs. 1 and 2) is secured to the support member 20 and provides a flat support surface for the apparatus 10.
The support member 20 is of metal or a plastic and carries on top wall 30 a left hand box 90 and a right hand box 100 as seen in Fig. 1. The left hand box 90 includes an insulating base plate 110, of a metal or plastic, secured to top wall 30 and a transparent enclosure, of plexiglass or the like, including (Figs. 1 and 2) left and right side walls 120 and 130, front and rear walls 140 and 150 and a top wall 160. The top wall 160 is a cover for the box 90 and is adapted to be lifted off the box by means of knob 162 to provide access to the interior thereof. The enclosure for box 90 is suitably secured to the base 110.
Box 90 is provided with a rotatable horizontal table 170 having a circular array of holes or apertures 180 in which fluid sample cups 190 are seated. The table is detachably secured to the upper end of a vertical post 200 so that tables with different numbers of holes or different sizes of holes or with other features can be secured to the post. The post 200 extends through and beneath the top wall 30 of the support member 20 (Fig. 2) where it is suitable connected to a small motor 210 which is used to rotate the post 200 and table 170. The motor 210 is secured to the lower surface 32 of the top wall 30 and is of a type which permits the post 200 or an extension thereof to extend through it to be driven thereby.
Adjacent to the rotatable table 170, referring to Figs. 1, and 2 is a hollow, tubular vertical post 220 having an aperture or slot 230 in its side wall. A horizontal arm 240 has one end inside post 220 and secured to a vertical rod 250 which is suitable mounted so that it can be driven vertically up and down. The lower end of the vertical rod 250 or an extension thereof passes through a small motor 260 secured to the lower surface 32 of the top wall 30. The lower end of the rod 250 carries a laterally projecting arm 263 which is positioned to operate with an optical sensor 280 positioned adjacent thereto.
Referring again to the horizontal arm 240, (Figs. 1, and 2,) the outer end thereof terminates in a small solid cylinder 243 which is oriented vertically and is provided with two through- holes 247 and 249 which communicate with a hollow tube 248 which extends downwardly from the solid cylinder in alignment with the holes 180 in table 170 and the sample cups therein. The hollow tube 248 is of a small diameter and is dimensioned so that it can enter a sample cup 190 and extend to about the bottom thereof to enter fluid therein.
The box 100 contains the same apparatus as box 90 as described above. The corresponding parts in box 100 carry the same reference numerals as the parts in the box 90 but primed.
The boxes 90 and 100 include means for applying electrical potential across the apparatus 10. This means includes a first wire electrode 360 having one end secured to a power input terminal 363. (Figs. 1 and 2) in the rear upwardly in the hollow tube 220 adjacent to the vertical rod 250 and out of the opening 230 in the side wall and through the hole 249 in cylinder 243 down through the tube 248 to the end thereof so that it can rest in a fluid in a sample cup when the apparatus 10 is in operation.
The electrical means also includes a similar wire electrode 360' secured to a power input terminal 365 in the rear wall 50 of the apparatus 10. This electrode follows a similar path through tube 250' and cylinder 243' into the tube 248' associated therewith for ultimate insertion into a sample cup. The electrodes 360 and 360' are preferably of platinum or the like and are adapted to carry the voltages used in operation of the invention. A power supply 367 is provided for connection to terminals 363 and 365 to electrodes 360 and 350' for providing the required voltages. Power supply 367 may also provide whatever other power is needed by the apparatus 10 such as for the motors 210, 210' and 260, 260'. Other auxiliary power supplies may be provided as desired.
In one embodiment of the invention, illustrated in Fig. 2, the power supply 367 may be of such small size that it can be mounted within support member 20 at any suitable location so that the apparatus 10 has its own self-contained power supply which may be manually or computer-controlled.
Referring to Figs. 1 and 2 an optical detector 290 for use in detecting material passing through a capillary tube which extends through the detector is seated on a support frame 300 secured to the top wall 30 of the support member 20 adjacent to the box 100. The apparatus 10 is designed to use a detector known as an on-column detector of the type which uses ultraviolet or fluorescent light in the detection process. Such detectors are made by ISCO of Lincoln, Nebraska and EM SCIENCE-HITACHI of Cherry Hill, New Jersey.
For use with the apparatus of the invention 10, modifications of the commercial detectors were made in the cuvette thereof. Other modifications might also be made.
The detector 290 is coupled to other apparatus 294 for providing a record of the detection operation and one such apparatus is the ISCO UA-5/V4 absorbance/fluorescence variable-wavelength detector or the EM SCIENCE-HITACHI L-4200/L-4000 UV/visible variable-wavelength detector which include a strip chart recorder and/or an integrator.
A rigid holder 308 is provided for supporting a capillary tube for the apparatus 10 between box 90 and box 100 (Figs. 1 and 2). This holder comprises a first hollow rigid tube 310 threadedly secured to one end of the cuvette of the optical unit of the detector 290 and supported along its length in a hole 320 in the side wall 130 of the box 90 and extending into the box 90. A second hollow rigid tube 330 is threadedly secured to the other end of the cuvette of detector 290 and is supported along its length in a hole 320 in the side wall 130 of the box 100 and extending into the box 100. The tubes 310 and 330 are aligned with each other and with the optical sensing element located within the detector 290.
The apparatus 10 utilizes a small-diameter, fused silica flexible quartz tube 310 through which ultraviolet light or fluorescent light used in the detector 290 can pass. The capillary tube, as noted above, may have inside diameter in the range of about 25 microns to about 200 microns and a length in the range of about 10 centimeters to about 100 centimeters. The capillary 350 is supported in the hollow rigid holder 308 and extends through the on-column detector 290 and through the optical sensing element or cuvette therein. At least the portion of the capillary which passes through the cuvette is transparent to the type of light used in the detector.
Since high voltages are used in operating the apparatus of the invention, it is clear that the capillary tube and the electrodes 360 and 360' should be spaced apart and insulated from each other.
In open-tubular capillary electrophoresis, using potential differences of about 5 to about 30 KV, an electroosmotic flow of buffer is generated in small bore capillaries which transport solute molecules (analytes) toward a detecting system. Charged analytes also migrate with or against this flow, depending on their mobilities and the intensity of the electroosmotic flow. In some cases, it is desirable to eliminate the electroosmotic flow effect and this can be achieved by providing in the carrier medium in the capillary certain substances such as methyl cellulose or certain electrolytes or polyacrylamide gels. The elimination of the electroosmotic flow effect permits charged particle migration due to the effect of applied voltages.
In the following description of the invention, it is assumed that precautions are taken to diminish electroosmotic flow in order to obtain controllable separations.
In general terms in the electrophoresis process as practiced with the apparatus 10, the capillary tube 310 is filled with a buffer solution which has a pH higher than the highest pK of the protein or other constituent in the sample being analyzed. This provides the desired negative charging of the capillary and the sample to be analyzed and the desired resultant flow of negatively charged sample particles toward the end of the capillary at which positive electrical potential is applied. In operation of the apparatus 10, ground potential is applied to electrode 360' and positive potential is applied to electrode 360. The capillary tube is filled with the desired buffer solution and then a quantity of a sample is injected into the high voltage positive (if a positive high voltage power supply is used) end of the capillary tube 350. The components of the sample become electrically negatively charged and each component takes on a different magnitude of charge as determined by the pH of the buffer solution and the migration takes place in the direction of the electroosmotic flow. The charged components of the sample become spaced apart in the capillary tube and with the proper potential applied, the more highly negatively charged components pass more quickly along the capillary through the on-column detector 290. The detector senses the passage of the charged particles and the recorder 284 prints a pulse for each type of charged particle with the pulse representing the position of the particles in the flowing stream and the quantity of the particles therein.
With respect to the injection of a sample into a capillary, if desired, the sample may be injected manually or in other suitable fashion. In one arrangement, the cups 190 and 190' can be positioned at different elevations, with cup 190' lower, to permit a quantity of sample or other fluid to flow into the sample end of the capillary.
As a modification of the invention, the apparatus 10 can be adapted to include means by which rather than raising and lowering the posts 250 and 250' and their associated apparatus, it raises and lowers either just specific sample cups or the entire tables 170 and 170'. In this embodiment of the invention, the motors 210 and 210' would be constructed to both rotate the posts 200 and 200' and to raise them and lower them vertically as required to raise and lower the tables 170 and 170'.
The capillary tube used in practicing the present invention, a capillary tube 645 includes several portions or segments of capillary each of which may have a different internal coating. The various coatings are selected to prevent macromolecules adsorption to the capillary walls and for separating the components of a sample whereby more efficient sample analysis can be achieved. Silane derivatives are one of the suitable coating materials. The coating materials used in this modification of the invention may be coated directly on the inner wall of the capillary or it may be provided in bulk form. In bulk form, masses of the chemicals would be inserted in the capillary by themselves or coated on an insulating support body of some kind such as spheres or the like.
The adjacent ends of the tube portions may be butted end to end and coupled together by sleeves which are secured by a suitable cement such as epoxy to the outer walls of the capillary portions.
An embodiment of the invention is shown in Fig. 3 and this embodiment is particularly useful for the analysis of biological fluids and thus for detecting substances in biological fluids such as serum, urine, cerebrospinal fluid, saliva, tears, etc. The embodiment now set forth is described in detail, including the chemistry required for binding of certain compounds to the capillary wall, in a paper entitled: "THE USE OF A CONCENTRATION STEP TO COLLECT URINARY COMPONENTS SEPARATED BY CAPILLARY ELECTROPHORESIS AND FURTHER CHARACTERIZATION OF COLLECTED ANALYTES BY MASS SPECTROMETRY" published in the Journal of Liquid Chromatography (Volume 14, Number 5, pages 997-1015, 1991). This paper is incorporated herein by reference.
Referring to Figure 3, an insert 760, known as an analyte concentrator, is provided in a capillary tube 770 which is used in place of capillary tube 310 of Figs. 1 and 2. The insert 760 includes porous end plates (or frits) 762 which permit fluid to flow therethrough. The end plates are formed from tiny glass beads. The insert 760 is a tube which contains glass beads 764, known as controlled-pore glass beads, which are coated with a desired chemical substance which will provide the desired reaction with a sample which passes through the analyte concentrator. The controlled pore glass beads are conveniently in the range of 200 to 400 mesh in size (3000 Å).
As noted glass beads 764 are coated with an antibody 766 (or antigen) which will attract and hold, with high affinity, a specific antigen 768 (or antibody) present in a sample, containing one or several substances, which passes through the capillary. Subsequent analysis provides information to the researcher as to the attracted antigen. As an example, porous glass beads have been coated with protein A from Staphylococcus aureus which has an affinity for immunoglobulins.
A further modification of the foregoing aspect of the invention using porous glass beads employs an analyte concentrator 772 which is a unitary structure which does not require porous glass end plates or frits. This structure shown in Figure 4 includes an annular wall or sleeve 774 of the diameter suitable to permit the structure to be coupled to or inserted between two portions of a capillary tube 770. Secured to the inner wall of the sleeve 774 is branched body 776 made up of a plurality of bodies, beads, platelets or the like made of porous glass material (or polymeric material having a suitable chemistry in its surface) and these are interconnected by means of glass strands 778 which also connect the bodies 780 to the inner wall of the sleeve 774. The bodies 780 may be of any shape and size for the intended purpose of being coated with an antibody.
It is noted that the binding of a substance to a surface or wall or beads or to any other structure within any part of the architecture of the analyte concentrator can be achieved for chemicals other than antibodies. These substances may have a high-affinity interaction (i.e. enzyme-substrate, lectin-carbohydrate, drug-receptor, ion-chelating agent, etc.), or may exert a strong repulsion to each other (equal surface charge, etc.).
Fig. 5 shows a modification of the invention wherein a freeform network of glass or plastic filaments 782 are secured together and the unitary structure thus formed can be coated with antibody (or other chemical substance) and inserted in a capillary tube 784.
In another modification of this aspect of the invention shown in Fig. 6, the equivalent of a large number of balls in a capillary tube is achieved by an insert 786 in a capillary tube 770. The insert is essentially a glass or plastic tube having a plurality of small diameter rod passages or through holes 788 which extend through the body and are coated with a chemical substance as described above. This form of the invention does not require porous end plates or frits to keep the body within the capillary tube.
In this form of the invention, referring to Fig. 6, a system using multiple capillary tubes 788 has the outlet ends of the capillaries coupled to a single capillary tube 783 by means of a suitable sleeve 785. This modification of the invention permits a larger amount of sample to be fed to a detector.
Fig. 7 shows a modification of an analyte concentrator which uses a mesh 801 of a chemical substance or polymer, such as acrylamide or agarose or the like, as the matrix for the antibody or antigen.
In operation of the inventions wherein structures are coated with an antibody, after a sample has passed through the structure and there has been binding of an antigen to the antibody structure, the capillary is washed to remove excess material and then the trapped antigens are removed and processed for study.
After many injections of samples, particularly those containing substances which have a tendency to stick to the walls of the capillary column such as serum or other biological fluids, it is necessary to restore the capillary column. Since commercially available fused-silica capillaries are inexpensive, one way to restore the capillary column is to replace it entirely.
Another alternative is to recycle the capillary column by a cleaning procedure. As seen in Fig. 8, a T-shaped connection 747 is made near the end of the capillary column with a small tube of material such as metal, glass, plastic, teflon or the like. This connection is now part of the capillary column. The connecting tube is attached to a valve 750 and a vacuum pump 752. This system can be operated through computer control allowing the column to be cleaned in a coordinated manner, i.e., by purging with potassium hydroxide, followed by deionized water and buffer aspirated from cups in the rotatable table 170 or other apparatus and discarded via a teflon port leading to a fluid trap. The capillary column is then ready for a new separation test.
The apparatus of the invention may also use a modified capillary which, as shown in Fig. 9, comprises a capillary cartridge 711. The cartridge includes a capillary cassette which comprises a coiled capillary tube 713 embedded in a body of metal, glass, plastic or the like. In coiled form, the capillary tube may be of any suitable length and it may contain various chemistries. The capillary cassette is held in a housing 721 made up of two plates of metal, glass, plastic or the like coupled by screws or the like. A temperature control fluid, which can be heated or cooled, can be circulated through the housing by way of inlet and outlet tubes 723 and 725. It is noted that the capillary cassette can be easily removed from the housing 721 and replaced by another cassette of different size or other characteristics.
The utility of the capillary assembly 711 as a readily replaceable cartridge which can provide capillaries of different lengths and chemistries will be clear to those skilled in the art. A mounting arrangement for the capillary assembly or cartridge 711 is illustrated in Fig. 10.

Claims

Capillary electrophoresis apparatus comprising a capillary tube (310, 645, 719) of the type which can be electrically charged, said capillary tube having first and second ends,

first means (170) at said first end of said capillary tube (310, 645, 719) providing a source of substance to be transmitted through said capillary tube,

second means (360) coupled to said apparatus (10) for applying electrical potential across said capillary tube (A) whereby a sample flows through said capillary tube and past a detector, and

said first means includes a rotatable table (170, 737) carrying a plurality of sample cups (190, 735) and a holder (220) for holding an end of said capillary tube (A) in operative relation with one of the said cups (190, 735) characterised by

an analyte concentrator (760, 772, 782, 786, 801) constituting an insert forming a portion of said capillary tube (A) and containing a support means (764, 780, 782, 788) carrying at least one chemical substance (760) of a type having a specific action with respect to constituent molecules contained within a sample flowing along said capillary (A) and either attracting a molecule for later elution or permitting a molecule to pass along the capillary tube.
The apparatus defined in claim 1 characterised in that said analyte concentrator(s) (760) comprises a tubular structure containing fluid-pervious end plates (762) and a plurality of small bodies (764) carrying antibody material or other chemical substance with affinity for each other (766) which is adapted to attract antigens or other chemical substances with affinity for each other in a sample fluid which passes through said analyte concentrator(s).
The apparatus defined in claim 1 characterised in that said analyte concentrator(s) (760) comprises a tubular structure containing fluid-pervious end-plates (762) and a plurality of small bodies (764) carrying a chemical substance(s) (766) which is adapted to repel other chemical substance(s) exerting a strong repulsion to said chemical substance(s) in a sample fluid which passes through said analyte concentrator(s).
The apparatus defined in claim 2 characterised in that said small bodies (764) comprise spheres of insulating material carrying said antibody material or other chemical substances with affinity for each other.
The apparatus defined in claim 1 characterised in that said analyte concentrator includes a plurality of thin plates (780) secured together and to the wall (774) of said capillary tube by filaments (778) of insulating material, said thin plates being coated with an antibody material or other chemical substance(s) with affinity for each other.
The apparatus defined in claim 1 characterised in that analyte concentrator comprises a plurality of filaments of plates secured together and disposed within said capillary tube, said filaments being coated with antibody material or other chemical substance(s) with affinity for each other.
An analyte concentrator for use with capillary electrophoresis apparatus characterised by

a tubular structure (760) for insertion in a capillary tube (A) and containing fluid-pervious end plates (762) and

a plurality of small bodies (764) which are disposed inside said tubular structure (760) for carrying antibody-material (766) which is adapted to attract antigens in a sample fluid which passes through said analyte concentrator(s), or

a plurality of small bodies (764, 780) which are disposed inside said tubular structure (760) for carrying a chemical substance(s) which is adapted to repel other chemical substance(s) in a sample fluid which passes through said analyte concentrator(s).
The apparatus defined in claim 7 characterised in that said small bodies comprise spheres of insulating material carrying said antibody material or other chemical substance(s) with affinity for each other (766).
The apparatus defined in claim 7 characterised in that said analyte concentrator includes a plurality of thin plates secured together and to the wall of said capillary tube by filaments (778) of insulating material, said thin plates being coated with an antibody chemical substance.
The apparatus defined in claim 7 characterised in that said analyte concentrator comprises a plurality of filaments of glass secured together and disposed within said capillary tube, said filaments being coated with an antibody material or other chemical substance(s) with affinity for each other.
capillary electrophoresis apparatus comprising a capillary tube means of the type which can be electrically charged, said capillary tube means having first and second ends,

first means (170) at said first end of said capillary tube (310, 645, 719) providing a source of substance to be transmitted through said capillary tube, and

second means (360) coupled to said apparatus (10) for applying electrical potential across said capillary tube (A) whereby a sample flows through said capillary tube and past a detector,

characterised in that said capillary tube means comprises an assembly (786) of a plurality of capillary tubes (788) having first and second ends,

second means comprising a single capillary tube (783) coupled to said second ends of said plurality of capillary tubes (788), and

a coupling sleeve (785) coupling together said single capillary tube (783) and said second ends of said capillary tubes (788).